Optimally decoupled robust control of MIMO plants with multiple delays

Abstract

A two-stage procedural design method is proposed for optimally decoupled, robust multivariable control of a (stable or unstable, minimum phase or nonminimum phase) plant with multiple delays. At the first stage, an optimal decoupler is designed for minimising the cross coupling effect. A modified characteristic loci method is next applied during the second stage to complete the design. The present approach distinguishes itself from the prevailing approaches such as LQG/LTR and H∞ design by its unique merits that: (i) the cross coupling effect is minimised; (ii) this approach could be applied to those plants with multiple delays; (iii) a straightforward robustness criterion is integrated into the design methodology which would consequently lead to robustly stable design; and (iv) this approach gives a necessary condition for the resultant controller to be both stable and of minimum phase. In a wide class of problems this condition is also sufficient for a stable, minimum phase controller.